The long-term objective of this project is to determine whether mild-to-moderate sleep-disordered breathing (SDB) leads to alterations in cardiac autonomic control that are detectable from nocturnal measurements of heart rate variability (HRV) and respiration. Since conventional spectral analysis of HRV can be seriously confounded by inter-subject differences or intra-individual changes in ventilation and ventilatory pattern during SDB, a recently developed algorithm will be used to compute "respiration-adjusted" spectral indices of HRV. This algorithm will be applied to a large sample of cardiorespiratory data derived from unattended home-based polysomnograms collected by the Sleep Heart Health Study. The specific goals of this study are to determine whether: (1) the conventional and "respiration-adjusted" spectral indices of HRV in quiet wakefulness are correlated with apnea-hypopnea index in individuals with severity of SDB; (2) chronic exposure to SDB alters the dependencies of the "respiration-adjusted" spectral indices of HRV on sleep state; (3) increasing severity of SDB leads to alterations in the amplitude and time-course of ultradian oscillations in the derived "respiration-adjusted" spectral measures of HRV. The application of this form of HRV analysis to a large database of polysomnographic data is likely to lead to a better understanding of the causal links that relate SDB to cardiovascular or cerebrovascular disease. As well, improved knowledge of the nocturnal rhythmicity of fluctuations in intrinsic autonomic activity and how this changes with chronic exposure to SDB could also provide important insights into the timing of acute cardiovascular events, such as myocardial infarction and stroke. [unreadable] [unreadable]